The purpose of this research is to develop a model system to study gene expression in normal and malignant animal cells. The system is the mouse plasmacytoma, and its normal cognate, the B-cell. The success of this study is highly dependent on the preparation and precise characterization of two specific molecular probes--the immunoglobulin mRNA and its complementary (cDNA). The mRNA will be prepared from different mouse myeloma tumors that have well-characterized, specific immunoglobulin products for both light and heavy chains. Therefore, excellent correlations could be obtained among different immunoglobulin classes regarding constant region gene structure and function, or analogously within the same class regarding variable regions. This could be achieved after establishing the biological activity and purity of the mRNA. Specific interest exists in studying heavy chain immunoglobulin gene structure and function because of their central role in the immune response.